1. Field of the Invention
The present invention relates to a low noise converter which smoothly power amplifies the rising edges and the falling edges of an input signal against an input with a repetitive waveform such as a rectangular waveform or a sine waveform etc. and which outputs the power amplified and smooth signal. The low noise converter of the present invention is available for power amplifiers like a switching regulator as one of DC stabilizing power sources, a DC-AC inverter for a dimmer, a converter for a back light of liquid crystal displays, an inverter applied the switching of a cathodic discharge lamp etc..
2. Description of the Prior Art
Conventionally, a switching regulator or the like outputs a predetermined DC output through ON/OFF switching, controlling, stabilizing, rectifying and smoothing a high voltage and a large current at a high speed, differently from the series regulator system of the power source. For this reason, various higher harmonic components are included in a voltage waveform and a current waveform, and many noise components are generated in the transient states at the ON/OFF switching. The level of a noise is 50.about.200 [mV] peak to peak value in general. These noise components appear as a signal noise appearing in a DC output signal, a back noise feedback into the input signal and also a radiant noise radiated in the air, and this results in one of the weak points of the switching regulator.
In order to eliminate the above noises, it needs a filter inserted in the input side or the output side, or a condenser arranged within the case. Further, a copper foil pattern on a printed circuit board or wiring of leading wires must be studied. Accordingly, the number of parts become large and the wiring operations are hard to homogenize, thus the operation efficiency has been lowered, and the manufacturing cost has been increased.
On the other hand, a converter with a Royer circuit which comprises a less number of parts and has a relatively simple circuit structure is well known. Nevertheless, the Royer circuit has a state wherein two switching transistors are simultaneous "ON", therefore, very large turn-on loss and cross-over loss-take place, besides, the available input frequencies could not cope with high-frequency waves.
Moreover, in the conventional DC-AC inverter, since an AC sine waveform is produced from a DC current by using a resonance circuit, the voltage fluctuation owing to a load has been large.
As the generation of the noise above mentioned is caused by a sudden rise or fall of a produced and power amplified waveform, it can be supposed that the fluctuation makes itself smooth to control the rapid varying.